If you're looking for something to give her just out of the blue instead of for a traditional gift-giving occasion, consider flowers. Yes, lots of people do them, but I've found very few women who don't enjoy getting flowers. If you don't want to go the traditional route of having a bouquet delivered, you oculd do something creative like giving it to her a bloom at a time over the course of the day or the week- finding a way to have flowers show up randomly and by surprise has worked for me before.